Environmental factors influencing the prevalence of a cutaneous ulcerative disease (red spot) in the sea mullet, Mugil cephalus L., in the Clarence River, New South Wales, Australia

Abstract

A cutaneous ulcerative disease (red spot) in sea mullet, Mugil cephalus L., from the Clarence River, New South Wales, Australia, was first reported in 1972. In this study, reports of disease outbreaks have been compared with rainfall and river flow records for the period from 1972 to 1988. Detailed disease prevalenee, rainfall, river flow and water quality data were compared for the period from 1985 to 1988. Significant correlations between weekly rainfall in the lower catchment and the prevalence of early stage lesions have been found. Progression to later stages of the disease occurred after rainfall and high river flows, which also caused rapid changes in various watcr-quahty eharaeteristies such as salinity, temperature, dissolved oxygen, pH and*turbidity. Organochlorine insecticide residues were not found to be associated with the disease in this area. The rainfall record since 1902 does not explain the absence of earlier reports of the disease. It is postulated that extensive structural developments for flood mitigation purposes and the increase in agricultural eultivation in the lower Clarence catchment during the last 20 years may be factors associated with the onset of the early stage of red spot disease. Fish in this early stage of the disease may then develop dermal ulcers under the stressful river conditions typically present during the autumn (high rainfall) season.

Emergence of Epizootic Ulcerative Syndrome in Native Fish of the Murray-Darling River System, Australia: Hosts, Distribution and Possible Vectors

“…This is consistent with most outbreaks of EUS, which tend to be associated with low and declining water temperatures and high rainfall [6], [9], [25], [33]. Virgona [16] reported significant correlation between rainfall and the prevalence of early stage lesions in sea mullet Mugil cephalus (L., 1758), and found that progression to later stage ulcers occurred after the high flows. Outbreaks of EUS in cultured B. bidyanus at the Grafton Aquaculture Centre occur only when water is pumped from the Clarence River during high flows or floods, and when fish in the river are known to have EUS [38].…”

Dermatitis, branchitis and mortality in empire gudgeon Hypseleotris compressa exposed naturally to runoff from acid sulfate soils

“…Lesions can be induced experimentally only if zoospores or hyphae are injected intramuscularly into fish or if fish with areas of abraded skin are exposed to zoospores (Roberts et al 1993, Callinan et al 1995b). Outbreaks of EUS in estuarine fish in the Richmond River and elsewhere have been associated spatially with tributaries draining ASS areas and temporally with rain events (Virgona 1992, Callinan et al 1993, 1995b, Sammut et al 1995. We suggest that propagules of the causative Aphanomyces sp.…”

Review of Biological Factors Relevant to Import Risk Assessments for Epizootic Ulcerative Syndrome (Aphanomyces invadans)

“…Further predisposing factors that have been suggested to be involved in EUS outbreaks include water quality–associated factors [i.e. drop in water salinity, low alkalinity and high ammonia, generally poor water quality, low oxygen levels (Khan et al., 2001; Virgona, 1992; Mohan et al., 1999; Asoka et al., 1999; Callinan et al., 1989)], exposure to toxins (Dykstra and Kane, 2000) and infection with ectoparasites, bacteria or viruses (Lilley et al., 1998). Most of these factors may lead to or be associated with skin injury, which may be the real predisposing factor.…”